what's the difference between 'repeat', 'extend' in image texture node?
I figured out. you can check the difference when you use mapping node with image texture and change the scale of an image on the object through mapping node. scale the image down with the mapping node by tweaking its scale option you'll see that extend just extends the image on the top of a object while repeat makes several same images on the top of an object.
from what I've figured out, you should scale the image down through mapping node or whatsoever.